1. Field of the Invention
This invention relates to an ink-jet recording method, and more particularly, to an ink-jet recording method adapted for multicolor recording.
1. Description of the Prior Art
Because of its quietness, fast recording capability, and adaptability to paper of ordinary grade, ink-jet recording is becoming increasingly popular; for example, one application is in computer terminal printers. Furthermore, the ink-jet method can be used to achieve multicolor recording using a plurality of ink nozzles. However, multicolor ink-jet recording involves problems not encountered in monochrome recording. In monochrome recording, one point on a recording paper is subjected to only one recording operation, and therefore satisfactory recording is obtainable most types of paper, e.g., fine paper, rolled paper for payment slips, and papers having greater degree of ink absorption than those previously mentioned. In multicolor recording, ink is squirted from two or more nozzles, and two or more (sometimes four) dots may be merged at one point on the recording paper. Unless the ink drop is absorbed quickly by the layer of paper, it merges with a subsequent ink drop applied on the same point of paper, causing flowing or flying of the ink and smearing thereof on the white background of the paper. If the recorded paper is handled carelessly, its surface may be rubbed to deface the image. Therefore, the use of recording paper having high ink absorption rate is particularly needed in multicolor recording.
Using a recording paper which absorbs ink well, an ink dot generally spreads and at the same time penetrates deep into the paper. For example, paper made as bulky as possible without using a sizing agent absorbs ink very well, and is therefore feasible for use in multicolor ink-jet printing. But the ink dots spread so much on this paper that they give low resolution, and ink penetrates the paper so deep that light scattering due to the interstices in the upper layer of the paper makes the resulting image whitish and less sharp. If four-color (cyan, magenta, yellow and Indian ink) recording is effected on paper of such high ink absorption, the depth of penetration of the first ink dot in the paper is enough to reduce its visibility from above, resulting in poor color reproduction.
As will be understood from the above discussion, to produce an image of high density, resolution and good color reproduction by multicolor ink-jet printing, the following three apparently incompatible requirements must be satisfied: (1) the coloring component of the ink should not show appreciable spreading on the recording paper used; (2) the greater part of said component should remain on the surface of the paper without penetrating deeply into the paper; and (3) the recording paper should have absorbing properties. Several developments have been made in order to achieve such objectives. For instance, Japanese Patent Application (OPI) No. 53012/77 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") discloses an ink-jet recording paper wherein raw paper of low size content is coated with a paint which penetrates the layer of paper. Japanese Patent Application (OPI) No. 49113/78 discloses an ink-jet recording paper wherein paper containing a fine powder of urea-formalin resin is impregnated with a water-soluble polymer. Japanese Patent Application (OPI) No. 74340/77 discloses an ink-jet recording paper having a specified degree of air permeability which absorbs ink in a specified period of time. However, the concept common to these three conventional techniques is to sacrifice ink absorption in order to provide high resolution and density. Although they achieve the intended object to some extent, the resulting paper does not absorb ink well and is not suitable for use in multicolor ink-jet recording. Therefore, there has been a demand in the industry for multicolor ink-jet recording paper satisfying the aforementioned three conditions.